college student summer job

I live in California.  My son is a fulltime college student in Michigan.  He had a summer job in Seattle and earned 32,000.  I understand I can still claim him as dependent since i am paying for most of his cost, but he has to file his own tax, correct?  Since his work was in Seattle, does he need to file state tax in California or in Washington?  His Seattle W2 listed his school dorm address as the employee address, if that matters.

 

Thanks

Bin